In order to ensure the functionality of electronic devices and systems, for example private computer networks, even in the event of mains failure, so-called UPS (uninterruptible power supply) systems are used. UPS systems ensure that, in the event of the mains voltage failing, the electronic devices or systems are supplied with emergency power via the UPS system. In other words, a UPS system ensures that, in the event of a fault in the mains supply, the system changes over from mains operation to emergency power operation. As soon as the mains supply starts operating again, the UPS system changes over from emergency power operation to mains operation.